1. Field of the Invention
The present invention relates to a tracer control system which permits an efficient quick-return motion of a tracer head from the terminating end of a trace path to the starting end of the next trace path.
2. Description of the Prior Art
In conventional tracer control systems, the starting and the terminating end of the trace path and the Z-axis position for quick return use are defined by limit switches. In the case of a one-way scan trace, a limit switch LX1 for the trace starting end, a limit switch LX2 for the trace terminating end and a Z-axis limit switch LZP for quick return use are provided at predetermined positions, as shown in FIG. 1. When it is detected by the operation of the limit switch LX2 that the tracer head has reached the terminating end of a trace path, the tracer head is quickly returned in the Z-axis direction. When it is detected by the operation of the limit switch LZP that the tracer head has risen up to a height Z at which the tracer head does not strike against a model, the tracer head is quickly returned in the X-axis direction. When it is detected by the operation of the limit switch LX1 that the tracer head has returned to the trace starting end, the tracer head is started to approach the model and when the tracer head arrives at a position spaced a predetermined distance from the model, the tracer head is subjected to deceleration control. When the tracer head moves into contact with the model, pick feed is performed and then the tracer head is started to trace the model surface in the X-axis direction.
The limit switch LZP is placed above the highest level of the model surface, preventing the tracer head from colliding with the model in its quick-return motion in the X-axis direction.
With such an arrangement, however, and also in the case where the model surface has only one peak, the tracer head is always raised higher than the peak in the Z-axis direction; accordingly, when the peak does not lie in the X-axis trace path, the quick-return motion of the tracer head becomes excessive. Further, the prior art system requires adjustment of the position of the limit switch LZP for each model and involves the mechanical limit switches, presenting a problem in terms of reliability.